1. Field of the Invention
The present invention relates to mobile vehicles and, more particularly, is directed to reconfigurable mobile vehicles having selectively magnetizable propulsion means that are capable of entry into a storage tank or infrastructure having constrained entry points and that are equipped with apparatuses to perform various visual and ultrasonic thickness inspection tasks for performing corrosion assessment thereof.
2. Description of the Invention Background
Nikolaus Otto is credited with inventing the internal combustion engine in 1877. In 1908, using the principles developed by Mr. Otto, Henry Ford introduced the Model T Ford, which has been called the first affordable automobile. Little did Mr. Otto and Mr. Ford know that their inventive prowess would spawn many of the billion dollar industries that we know today.
For example, with the development of the automobile came the need for petroleum refineries and filling stations for supplying gasoline to power the automobile between destinations. Soon, filling stations began to appear all over the country. Today, there are thousands of filling stations across the United States alone.
Such filling stations typically store gasoline in steel underground tanks that are periodically replenished by fuel transport trucks that transport the fuel from similar aboveground storage tanks located at refinery to the filling station. Over the years, due to the corrosive influence of the surrounding environment, most underground and aboveground fuel storage tanks periodically develop leaks and ruptures in the walls thereof. Often, such tank leaks go undetected permitting gasoline to be slowly leached into the surrounding soil. Initially, such leaks go undetected until they become noticeably larger. However, once it is apparent that the tank is leaking, it is difficult, if not impossible using known methods and techniques, to determine the exact location of the leak without first emptying the tank.
As such, a variety of tank inspection methods have been developed. One such method involves emptying the tank and sending human inspectors into the tank in an effort to identify and repair the leak and to ascertain the tank's fuel holding integrity. That method, however, is fraught with many inaccuracies, dangers, and disadvantages, In particular, the inspectors must be equipped with explosion proof lights and inspection equipment that can be safely operated in an atmosphere containing explosive vapors and gases. In addition, the inspectors must wear respirators to protect them from inhaling harmful vapors. That additional cumbersome equipment, however, tends to hinder their ability to maneuver within the tank. In addition, this tank inspection method is very time consuming and, because the tank must be emptied before the inspection can take place, the tank cannot be used while the inspection thereof is being conducted.
Another tank inspection method involves first removing the tank's contents and thereafter further evacuating the tank. After a certain amount of vacuum is drawn within the tank, vacuum gages can be used to monitor whether there is a loss of vacuum due to air infiltration through a leak in the tank. In the alternative, sensitive listening devices may be placed within the tank to detect the inrush of air therein. That method, however, is incapable of analyzing the overall structural integrity of the tank.
Another tank inspection method involves removing the fuel from the tank and lowering a camera on a cable to view the tank's interior. This method also lacks the capability of analyzing the structural integrity of the tank's walls to identify other deteriorating portions thereof. Yet another method involves removing the tank from the ground so that its outer perimeter can be inspected. That method, however, is ineffective for detecting leaks in double-walled tanks because the integrity of the interior wall cannot be ascertained from a visual or ultrasonic inspection of the exterior tank wall.
It will be appreciated that the above-described problems are not limited to underground or above-ground storage tanks that contain gasoline or other petroleum products. Such problems may also be encountered with tanks and structures containing a variety of other hazardous or contaminated waste materials. It will be further appreciated that dams and penstocks are also plagued with similar inspection problems. In particular, those structures typically must be inspected by divers or they must be decommissioned and drained before they can be inspected.
A variety of vehicles and robots have been developed for conducting various operations in hostile or hazardous environments. Some of those vehicles are manned such as the vehicle disclosed in U.S. Pat. No. 4,645,023 to Rea et al. That vehicle, while suited for travel on a variety of terrain configurations and conditions, is ill-suited for use inside of an enclosed tank where human access is prohibited. Furthermore, that vehicle could not traverse the vertical walls or ceiling of the vessel to perform inspections thereof.
Other apparatuses have been developed for cleaning the interior of enclosed vessels such as storage tanks. In particular, the mobile, remotely powered robot disclosed in U.S. Pat. No. 4,817,653 to Krajicek et al. is equipped with a spraying device and is adapted to ride upon the floor of the tank. To use that apparatus, however, the tank must first be substantially emptied and a robot entry way must be provided through the side of the tank. The component parts of the robot are then passed through the entry way into the tank wherein they are reassembled and operated by personnel located within the tank. That device is also ill-suited for use in tanks or vessels where, due to the nature of the material stored therein, human access is prohibited. In addition, the Krajicek apparatus could not be used to inspect storage tanks that may be substantially weakened by providing therein an entryway large enough to permit the passage of the robot's components therethrough.
Other robots adapted to operate in hostile environments are known. For example, U.S. Pat. No. 4,932,831 to White et al. and U.S. Pat. No. 5,022,812 to Coughlan et al. disclose track-propelled robots that can be operated from a remote location by means of a tether line that is attached to the robot. Those apparatuses, while somewhat compact, are not collapsible to the extent necessary to permit them to be entered into an enclosed area through a small existing manway or pipe riser therein. In addition, those vehicles cannot traverse along the vertical sides and ceiling of the tank or vessel to perform inspections thereof.
Still other single tracked vehicles are known that could be adapted for entry into a vessel through a small opening therein. For example, U.S. Pat. No. 3,548,962 to Best and U.S. Pat. No. 4,909,341 to Rippingale et al. disclose single tracked articulated vehicles that are capable of assuming a variety of different configurations. Those vehicles, much like the vehicles disclosed in the above-mentioned patents, cannot travel around the vertical walls and ceiling of a tank or vessel to perform various inspection tasks.
A wall-crawling vehicle has been developed, however, by Naito et al. and is disclosed in U.S. Pat. No. 4,828,059. That apparatus comprises a dual or triple-tracked vehicle that, due to its large size, would be unable to enter an enclosed vessel through a small existing manway or pipe riser therein. In addition, the vehicle obtains it wall-crawling abilities by a plurality of permanent magnets attached to the outer perimeter of the crawler tracks. The apparatus is equipped with a guide device adapted to selectively cause the magnets to move between positions wherein they can magnetically engage the wall surface and a position wherein they do not magnetically engage the wall surface. However, if during the course of operation, operational power should be lost to the guide device, the permanent magnets would remain magnetically attached to the walls of the vessel, thus, making it difficult, if not impossible, to retrieve the apparatus from the vessel. In addition, this apparatus would be ill-suited for travel in a vessel containing some loose magnetic material, as that material could collect around the track and frame and hamper the operation of the guide device.
Thus, there is a need for a vehicle that can enter an enclosed structure through a constrained entry point and be safely operated by personnel located outside of the structure to perform a variety of inspection and other tasks within the structure. There is a further need for a vehicle that can safely perform a variety of tasks within a vessel containing liquid material without first removing the material from the vessel. There is still another need for a remotely operable vehicle that can enter an enclosed vessel through a constrained entry point and travel along the vessel walls, bottom and ceiling to assess the structural integrity of the vessel.